The superimposition of graphic elements such as textual or graphical ‘logos’ onto video images is common. Typically the objective is to ‘brand’ or identify a particular channel or video source, or simply to add advertising material. The superimposed elements are usually located at a fixed position relative to the image frame; they may be opaque or transparent, stationary or moving. However, the superimposed elements are intended to be recognised by a viewer, and therefore will have predetermined form unrelated to the images to which they are applied. The term logo will be used henceforth in this specification to refer to these superimposed elements.
It is highly advantageous for the presence of particular logos to be identified in an automatic monitoring system for a video content production and/or distribution system. This is essentially a pattern recognition problem, which is complicated by the completely unknown nature of the background behind the logo. And, a given logo pattern to be recognised may be a sampled image with an unknown spatial relationship to the sampling of the image in which it has to be detected.
Known methods that can be used to detect logos in video images include correlation, either in the spatial domain, or the spatial frequency domain. There are a number of algorithms for identifying ‘feature points’ or singularities in images; the positions of feature points in an image in which a logo may be present can be compared with the positions of feature points in an image comprising only the logo to be detected.
Known techniques require significant processing resources that limit their application. There is thus a need for an alternative approach based on a simpler method of image analysis.